CrotalariaNew Holland Rattlepodbuds with Argina astraeacomes from the Greek κροταλον (krotalon), a rattle or castanets, referring to the seed pods; novæ-hollandiæ is botanical Latin for ‘of New Holland’, an earlier name for Australia.

On Magnetic Island we are very rich in Crotalaria – 7 species are described on this website. Most rattlepods are trifoliate, but this one has single leaves. There are 3 subspecies of the New Holland Rattlepod: ssp. crassipes, ssp. lasiophylla, and ssp.novae-hollandiae, and I think that the one found on the island belongs to the last of them. In 2010 I noticed two stands of the plant, one on the other side of the road from the habitat reserve in Nelly Bay, and the other on the Picnic Bay foreshore.

This is a small shrub growing 20–100 cm high. It may be glabrous, or have greyish appressed hairs, and is found in sandy soils in a variety of habitats. It grows quite densely, with oval-shaped leaves, long racemes of yellow pea flowers, and 2–3 cm long seed pods.

The plants of this genus contain pyrrolizidine alkaloids. These toxins accumulate in the liver and produce long-term damage which is often fatal. Horses and cattle are more susceptible to poisoning than sheep, but sheep have been poisoned by Crotalaria eremea (bluebush pea) in western Queensland. Poisoned horses develop a condition called ‘walk-about disease’ or ‘Kimberley horse disease’. They become unaware of their surroundings and wander blindly. A major cause of this poisoning is Crotalaria crispata, a small plant common in the Kimberley region of Western Australia. Other Crotalaria species cause the disease in the remainder of tropical Australia. Cattle infected by the toxins gradually lose weight and die. In central and northern Queensland an unusual disease of horses is caused by two other species of Crotalaria, Crotalaria aridicola(Chillagoe horse poison) and Crotalaria medicaginea (trefoil rattlepod). Horses often develop a taste for these plants, which damage the oesophagus and produce ulceration severe enough to stop the horse from swallowing food.

flowerspodsUnder normal circumstances, native plant-eaters (including mammals and insects) have developed ways of avoiding being poisoned. Some insects have developed to a point where plant toxins form part of their own defence, storing the toxins from the plant. The larvae have the toxins in their bodies, and this deters their would-be predators – a caterpillar that feeds on a rattlepod will itself be toxic to anything that eats the caterpillar. Many bush creatures (brush-tailed possums, bush rats, western grey kangaroos, red kangaroos, eastern grey kangaroos, for instance), having developed an efficient chemical detoxication method in the liver, happily graze on plants that will poison horses and cattle.

Because plant-eaters are so well adapted to their natural environments, poisoning occurs only when those environments are seriously disturbed, say by drought or by human interference, and animals are forced to leave their accustomed ecological niches to feed on dangerous plants. Koalas are believed to have been poisoned by cyanide while feeding on fresh young regrowth of manna gums, Eucalyptus viminalis, after bushfires in Victoria.

The various Crotalaria species are food plants for several caterpillars, including those of: